Question

观察下列各式:①(a+b)=a+b;②(a+b)^2=a^2+2ab+b^2;③(a+b)^3=a^3+3a^2b+3a

Answer 1

(a+b)^7=a^7+7a^6b+21a^5b^2+35a^4b^3+35a^3b^4+21a^2b^5+7ab^6+b^7