A quadratic function is defined by k(x) = (x - 100)(x + 20). [br][br]How would you explain to a friend who is absent today how to use the equation to:[br][br][list=1][*]Find the zeros of the function?[/*][*]Find the x-intercepts of the graph?[/*][*]Find the x-coordinate of the vertex without graphing?[/*][*]Find the y-coordinate of the vertex without graphing?[/*][*]Find the y-intercept of the graph?[/*][/list]
1. Find the value of x that makes each parenthesis equal to 0, x = 100, x = -20[br]2. Write the zeros as points where the y-coordinate is 0, (100, 0) and (-20, 0)[br]3. It's halfway between the x-intercets, add the x-value of the xintercepts together and divide by 2, (100+ -20)/2 = 80/2 = 40[br]4. Plug the x-value of the vertex into the equation, k(40) = (40 - 100)(40 + 20) = (-60)(60) = -3600[br]5. Mutiply the factrors of the equation to get standard form (ax[sup]2[/sup] + bx + c), the y-intercept is c (and x = 0), k(x) = x[sup]2[/sup] - 80x - 200 so (0, -200).