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find the x-intercept: \( y=x^{2}-4 x-5 \)

Ask by Norris Potter. in China
Jan 23,2025

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Answer

函数 \( y = x^{2} - 4x - 5 \) 的 x 截距是 \( (5, 0) \) 和 \( (-1, 0) \)。

Solution

要找到函数 \( y = x^{2} - 4x - 5 \) 的 x 截距,需要令 \( y = 0 \) 并解方程: \[ 0 = x^{2} - 4x - 5 \] 使用求根公式 \( x = \frac{-b \pm \sqrt{b^{2} - 4ac}}{2a} \),其中 \( a = 1 \),\( b = -4 \),\( c = -5 \): \[ x = \frac{4 \pm \sqrt{(-4)^{2} - 4 \cdot 1 \cdot (-5)}}{2 \cdot 1} \] \[ x = \frac{4 \pm \sqrt{16 + 20}}{2} \] \[ x = \frac{4 \pm \sqrt{36}}{2} \] \[ x = \frac{4 \pm 6}{2} \] 因此,x 的值为: \[ x = \frac{4 + 6}{2} = 5 \] \[ x = \frac{4 - 6}{2} = -1 \] 所以,函数的 x 截距为 \( (5, 0) \) 和 \( (-1, 0) \)。

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Mind Expander

To find the x-intercept of the equation \( y = x^2 - 4x - 5 \), set \( y \) to 0 and solve for \( x \). So, the equation becomes \( 0 = x^2 - 4x - 5 \). Factoring gives us \( (x - 5)(x + 1) = 0 \). This means \( x - 5 = 0 \) or \( x + 1 = 0 \). Thus, the x-intercepts are \( x = 5 \) and \( x = -1 \). Now, for a fun nugget of trivia: this quadratic function actually represents the shape of a parabola! In this case, it opens upwards because the coefficient of \( x^2 \) is positive. Imagine this parabola gracefully curving up, with its hands reaching down to touch the x-axis at those beautiful points (5,0) and (-1,0). You can think of the x-intercepts as the "landing spots" where the graph touches the x-axis, and they mark the points where the output (y) is zero. These intercepts play a crucial role in graphing and analyzing polynomial functions, giving insight into the function's behavior.

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