先化简,再求值:((3x-7)的2次方-(x+5)的2次方)/(4x-24),其中x=2
问题描述:
先化简,再求值:((3x-7)的2次方-(x+5)的2次方)/(4x-24),其中x=2
答
[(3x-7)^2-(x+5)^2]/(4x-24)
=(3x-7-x-5)(3x-7+x+5)/[4(x-6)]
=(2x-12)(4x-2)/[4(x-6)]
=4(x-6)(2x-1)/[4(x-6)]
=2x-1
=2*2-1
=4-1
=3