Question

помогите, очень срочно

Answer 1

7)1/b^2-1/a^2=(a^2-b^2)/a^2b^2, ab/(a-b )*(a-b)(a+b)/a^2b^2=(a+b)/ab.   8) (7^(k+1)-2*7^k)/5*7^(k-1)=7^k(7-2)/(5*7^(k-1))=7^(k-1)*7/7^(k-1)=7.