先化简,再求值大侠们1求5x^2-[3y^2+7xy]+[2y^2-5x^2]的值,其中x=0.1,y=-0.22求15a^2-{-4a^2+5a-8a^2-[2a^2-a]+9a^2-3a｝的值,其中a=-1又2分之1

Question

先化简,再求值 大侠们
【1】求5x^2-[3y^2+7xy]+[2y^2-5x^2]的值,其中x=0.1,y=-0.2 【2】求15a^2-{-4a^2+【5a-8a^2-[2a^2-a]+9a^2】-3a｝的值,其中a=-1又2分之1

Answer 1

5x^2-[3y^2+7xy]+[2y^2-5x^2]
=5x^2-3y^2-7xy+2y^2-5x^2
=-y²-7xy
=-0.04+7*0.02
=0.1
4a^2+【5a-8a^2-[2a^2-a]+9a^2】-3a｝
=4a^2+5a-8a^2-2a^2+a+9a^2-3a
=3a²+3a
=27/4-9/2
=9/4