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question:Given a hyperbola frac{x^2}{a^2} frac{y^2}{b^2} = 1 (a > 0, b > 0) whose asymptotes intersect with the directrix of the parabola y^2 = 4x at points A and B, and let O be the origin of the coordinates. If the area of triangle AOB is 2sqrt{3}, find the eccentricity e of the hyperbola.
answer:Let's begin with the equation of the asymptotes of the hyperbola, which are, y = pmfrac{b}{a}x. The directrix of the parabola y^2 = 4x is x = -frac{1}{4} times 4 = -1. Points A and B are the intersection points of the asymptotes with the directrix, which means they lie on the line x = -1. The coordinates of points A and B can therefore be written as: A(-1, frac{b}{a}), quad B(-1, -frac{b}{a}). Now, we can calculate the area S_{triangle AOB} using the formula for the area of a triangle with base and height: S_{triangle AOB} = frac{1}{2} times |OB| times |OA| = frac{1}{2} times 2 times frac{b}{a} = frac{b}{a}. Setting this equal to the given area, we have: frac{b}{a} = 2sqrt{3}. Squaring both sides gives: frac{b^2}{a^2} = 12. Since for a hyperbola, c^2 = a^2 + b^2, we can relate c^2 and a^2 as follows: frac{c^2 - a^2}{a^2} = 12 Rightarrow frac{c^2}{a^2} = 12 + 1 = 13. The eccentricity e of the hyperbola is defined as e = frac{c}{a}. Thus, we find: e = sqrt{frac{c^2}{a^2}} = sqrt{13}. Therefore, the eccentricity of the hyperbola is boxed{sqrt{13}}.
question:Given a positive integer ( n ) and a positive number ( M ), for all arithmetic sequences ( a_1, a_2, a_3, ldots ) that satisfy the condition ( a_1^2 + a_{n+1}^2 leq M ), find the maximum value of ( S = a_{n+1} + a_{n+2} + cdots + a_{2n+1} ).
answer:1. **Identify relevant equations and expression for S:** Given a sequence that is an arithmetic progression (AP), if (a_1) is the first term and (d) is the common difference, then the term at position (n+1) can be written as: [ a_{n+1} = a_1 + nd ] 2. **Determine the (2n+1)th term:** The (2n+1)th term in the sequence can be written as: [ a_{2n+1} = a_1 + 2nd ] Substitute (d) from the first equation: [ a_{2n+1} = a_1 + 2n left(frac{a_{n+1} - a_1}{n}right) = a_1 + 2(a_{n+1} - a_1) = 2a_{n+1} - a_1 ] 3. **Expression for S:** The sum of terms from a_{n+1} to a_{2n+1} is given as (S): [ S = a_{n+1} + a_{n+2} + ldots + a_{2n+1} ] The sum of n+1 terms in an AP is: [ S = frac{(n+1)}{2} left( a_{n+1} + a_{2n+1} right) ] Substitute (a_{2n+1} = 2a_{n+1} - a_1): [ S = frac{(n+1)}{2} left( a_{n+1} + (2a_{n+1} - a_1) right) = frac{(n+1)}{2} left(3a_{n+1} - a_1 right) ] 4. **Using the condition (a_1^2 + a_{n+1}^2 leq M):** Use the identity to relate this to the derived sequence sums: [ a_1^2 + a_{n+1}^2 leq M ] Applying the Cauchy-Schwarz inequality in the context of the problem, we get: [ M geq a_1^2 + a_{n+1}^2 geq frac{1}{10} left[(3a_{n+1} - a_1)^2 + a_{n+1}^2 right] ] 5. **Simplify the inequality:** We adjust the inequality to find the maximum bound: [ a_1^2 + a_{n+1}^2 geq frac{1}{10}(3a_{n+1} - a_1)^2 ] It implies: [ sqrt{10M} geq 3a_{n+1} - a_1 ] 6. **Substitute and isolate (S):** From the inequality, noting that the maximum possible value will be achieved when: [ sqrt{10M} = 3a_{n+1} - a_1 ] Substituting back to our expression for (S) gives: [ S leq frac{(n+1)}{2} sqrt{10M} ] 7. **Conclusion:** We have: [ S_{text{max}} = frac{(n+1)}{2} sqrt{10M} ] Therefore, the maximum value of S is: [ boxed{frac{n+1}{2} sqrt{10M}} ]
question:Find the equation of the tangent line to the curve y=sin x+e^{x} at x=0. A) x3y+3=0 B) x2y+2=0 C) 2xy+1=0 D) 3xy+1=0
answer:First, let's find the derivative of the given function y=sin x+e^{x} with respect to x. begin{aligned} y' &= frac{d}{dx}(sin x + e^x) &= frac{d}{dx}(sin x) + frac{d}{dx}(e^x) &= cos x + e^x end{aligned} Next, we need to find the slope of the tangent line at x=0. We do this by plugging x=0 into the derivative expression. begin{aligned} k &= y'(0) &= cos(0) + e^0 &= 1 + 1 &= 2 end{aligned} Now that we know the slope of the tangent line, we can use the point-slope form of a linear equation to find the equation of the tangent line. The point (0, 1) is on the curve because y(0) = sin(0) + e^0 = 1. Therefore, the equation of the tangent line is: begin{aligned} y - y_1 &= m(x - x_1) y - 1 &= 2(x - 0) y &= 2x + 1 end{aligned} Converting this equation to the standard form: boxed{2x - y + 1 = 0} The answer is (C).
question:bag A, there are 8 white balls and 4 red balls, and in bag B, there are 6 white balls and 6 red balls. These balls are identical except for their colors. If one ball is randomly selected from each bag, which of the following conclusions is correct? A: The probability of the two balls having the same color is frac{1}{2}. B: The probability of neither ball being red is frac{1}{3}. C: The probability of at least one red ball is frac{2}{3}. D: The probability of exactly one red ball among the two balls is frac{1}{2}.
answer:To solve the problem, we start by analyzing each option given in the question one by one. **Option A: The probability of the two balls having the same color** From bag A, the probability of drawing a white ball is frac{8}{12} and from bag B, it is frac{6}{12}. Therefore, the probability of both balls being white is frac{8}{12} times frac{6}{12}. Similarly, the probability of drawing a red ball from bag A is frac{4}{12}, and from bag B, it is frac{6}{12}. Thus, the probability of both balls being red is frac{4}{12} times frac{6}{12}. The total probability of the two balls having the same color is the sum of the probabilities of both being white and both being red, which is frac{8}{12} times frac{6}{12} + frac{4}{12} times frac{6}{12} = frac{1}{2}. Therefore, option A is correct, and we have P_{text{same color}} = boxed{frac{1}{2}}. **Option B: The probability of neither ball being red** The probability of drawing a white ball from both bags is frac{8}{12} times frac{6}{12}. However, the calculation provided in the solution for option B seems to be incorrectly addressing a different scenario. The correct calculation for neither ball being red (both balls being white) should be directly calculated as frac{8}{12} times frac{6}{12} = frac{1}{3}, not related to the provided calculation. Thus, option B's calculation is not aligned with the provided scenario. The standard solution may have a misinterpretation for this option. **Option C: The probability of at least one red ball** The probability of at least one red ball is the complement of the probability of no red balls (both white), which is correctly calculated as 1 - left(frac{8}{12} times frac{6}{12}right) = frac{2}{3}. Therefore, option C is correct, and we have P_{text{at least one red}} = boxed{frac{2}{3}}. **Option D: The probability of exactly one red ball among the two balls** This was calculated similarly as for option A, and it seems there was a confusion in the explanation. The correct approach to find the probability of exactly one red ball should consider the cases where one bag gives a red ball and the other gives a white ball. However, the given solution repeats the calculation for option A. The intended calculation should account for the combinations of one red and one white ball from each bag, which is not clearly described in the provided solution. **Correct Options Analysis** Given the discrepancies and the direct calculation for option A, the correct options based on the provided explanation and corrections would indeed suggest that options A and C are correctly calculated, with A showing the probability of the two balls having the same color as boxed{frac{1}{2}} and C showing the probability of at least one red ball as boxed{frac{2}{3}}. Option D's explanation matches that of A, which suggests a possible clerical error rather than a distinct scenario calculation. Given these insights and corrections, the correctly interpreted options are A and C, with D being subject to clarification regarding the exact calculation intended for exactly one red ball.