Question

（a+b)^4=?

Answer 1

=(a方+b方+2ab)^2=a四次方+b四次方+4a方b方+2a方b方+4a三次b+4ab三次=a四次方+b四次方+6a方b方+4a三次b+4ab三次

记公式或挨个乘(a+b+c)^2=a^2+b^2+^2+2ab+2ac+2bc

Answer 2

(a+b)^4=(a+b)^2*(a+b)^2=(a^2+2ab+b^2)(a^2+2ab+b^2)=a^4+b^4+4a^3b+6a^2b^2+4ab^3