工夫して計算をします! ⑴ (a+b+2)(a+b+3) -(a+b+5)(a+b) a+b=m (m+2)(m+3) -(m+5)(m) =(m²+5m+15) -(m²+5m) =m²+5m+15 -m²-5m =+15 答え 15 ⑵ (2x+y-z)²+(x+y-z)(x-y+z) y-z=m (2x+y-z)²+(x+y-z)(x-(y-z)) =(2x+m)²+(x+m)(x-(m)) =(2x+m)²+(x+m)(x-m) =(4x²+m²+4xm)+x²-m² =4x²+m²+4xm+x²-m² =4x²+4xm+x² =5x²+4xm =5x²+4x(y-z) =5x²+4xy-4xz ⑶ (2x+3y+5)(2x-y+5) +(2x+5y+5)(2x-7y+5) 2x+5=m (m+3y)(m-y) +(m+5y)(m-7y) =(m²+2ym-3y²) +(m²-2ym-35y²) =m²+2ym-3y² +m²-2ym-35y² =2m²-38y² 2x+5=m (4x²+20x+25)=m² 2m²-38y² =2(4x²+20x+25)-38y² =8x²+40x+50-38y² =8x²+40x-38y²+50