已知f(x1)=2x²-3x1,f(-1)的值是_____
f(x+1) = 2x² - 3x + 1
方法1、直接带入
x + 1 = -1,x = -2;
f(-1) = 2(-2)^2 - 3(-2) + 1 = 8 + 6 + 1 = 15;
方法2、换元
x + 1 = u,x = u - 1;
f(u) = 2(u-1)^2 - 3(u-1) + 1 = 2u^2 - 7u + 6
f(-1) = 2(-1)^2 - 7(-1) + 6 = 2 + 7 + 6 = 15 。
热门标签: