(1).(2x+5y)^2
=(2x)^2+2*2x*5y+(5y)^2
=4x^2+20xy+25y^2
(2).(1/3m-1/2)^2
=(1/3m)^2-2*1/3m*1/2+(1/2)^2
=1/9m^2-1/3m+1/4
(3).(-2t-1)^2
=(2t+1)^2
=(2t)^2+2*2t*1+1^2
=4t^2+4t+1
(4).(1/5x+1/10y)^2
=(1/5x)^2+2*1/5x*1/10y+(1/10y)^2
=1/25x^2+1/25xy+1/100y^2
(5).(7ab+2)^2
=(7ab)^2+2*7ab*2+2^2
=49a^2b^2+28ab+4
(6).(-cd+1/2)^2
=(-cd)^2-2*cd*1/2+(1/2)^2
=c^2d^2-cd+1/4
计算:(a+b+c)^2=a^2+b^2+c^2+2ab+2bc+2ac