Question

化简,再求值2(x+1)的2次方-5(x+1)(x-1)+3(x-1)的2次方 其中x=7.5

Answer 1

2(x+1)²-5(x+1)(x-1)+3(x-1)²
=[(x+1)-(x-1)][2(x+1)-3(x-1)]
=2(5-x)
=2×(5-7.5)
=2×(-2.5)
=-5

Answer 2

2(x+1)的2次方-5(x+1)(x-1)+3(x-1)的2次方

=(2x+2-3x+3)(x+1-x+1）
=（5-x)(2)
=2(-2.5)
=-5

Answer 3

2(x+1)^2-5(x+1)(x-1)+3(x-1)^2
=[(x+1)-(x-1)][2(x+1)-3(x-1)]
=2(2x+2-3x+3)
=2(-x+5)
=-2x(x-5)

Answer 4

2(x+1)^2-5(x+1)(x-1)+3(x-1)^2

=2x^2+4x+2-5x^2+5+3x^2-6x+3
=-2x+5
因为x=7.5所以
原式=-2*7.5+5=-10

Answer 5

2(x+1)^2=2(x^2+2x+1)=2x^2+4x+2
代入x=7.5,原式=2x7.5^2+4x7.5+2=112.5+30+2=144.5
-5(x+1)(x-1)+3)=(-5x-5+3)(x-1)=(-5x-2)(x-1)
((-5x-2)(x-1))^2=(25x^2+20x+4)(x^2+2x+1)=25x^4+70x^3+69x^2+28x+4
代入x=7.5，原式=((-5x7.5-2)(7.5-1))^2=(39.5x6.5)^2=65920.5625