Expand:
(1)(a+2)(a−1)
(2) (m−4)(m+6)
(3) (p+8)(p−3)
(4) (13+x)(13−x)
(5) (3x+4y)(3x+5y)
(6) (9x−5t)(9x+3t)
(7) (m+23)(m−73)
(8) (x+1x)(x−1x)
(9) (1y+4)(1y−9)
It is known that,
(x+a)(x+b)=x2+(a+b)x+ab
(1)
(a+2)(a−1)=a2+(2+−1)a+(2×−1)=a2+1(a)−2=x2+a−2
(2)
(m−4)(m+6)=m2+(−4+6)m+(−4×6)=m2+2m−24
(3)
(p+8)(p−3)=p2+(8+−3)p+(8×−3)=p2+5p−24
(4)
It is known that, (a+b)(a−b)=a2−b2
(13+x)(13−x)=(13)2−x2=169−x2
(5) (3x+4y)(3x+5y)=(3x)2+(4y+5y)3x+(4y×5y)=9x2+(9y×3x)+20y2=9x2+27xy+20y2
(6) (9x−5t)(9x+3t)=(9x)2+(−5t+3t)9x+−(5t×3t)=81x2+(−2t)9x−15t2=81x2−18xt−15t2
(7) (m+23)(m−73)=m2+(23+−73)m+(23×−73)=m2−(5m)3−149
(8)
It is known that
(a+b)(a−b)=a2−b2
(x+1x)(x−1x)=x2−1x2
(9)
(1y+4)(1y−9)=1y2+(4+−9)1y+(4×−9)=1y2+−5y−36