Question

先化简.再求值:(8a的平方+4a+1)(-8a的平方+4a-1)其中a=2分之1

Answer 1

原式=(a^2+4a+1)(-8a^2+4a-1)

=(4a)^2-(8a^2+1)^2

=16a^2-64a^4-16a^2-1

=-64a^4-1

当a=1/2时

原式=-64(1/2)^4-1

=-4-1

=-5