1、
1/2*6*8=1/2*10*h
h=4.8
2、
3(x-2y)的平方-5(x-2y)+6
=(3(x-2y)-2)(3(x-2y)-3)
=-20*(-21)
=420
3、
(x+2)(x-6)+16
= x^2-4x-12+16
=x^2-4x+4
=(x-2)^2
4、
设a=1.345
则a-1=0.345
2a=2.69
1.345*0.345*2.69-1.345的平方-1.345*0.345的平方
=a*(a-1)*2a-a^2-a(a-1)^2
=2a^2(a-1)-a^2-a(a-1)^2
=a^2(2a-1-1)-a(a-1)^2
=2a^2(a-1)-(a^2-a)(a-1)
=(2a^2-a^2+a)(a-1)
=(a^2+a)(a-1)
=a(a+1)(a-1)
=1.345*2.345*0.345
=1.088138625