Verified answer

a+b=4

ab=-6

(a-b)²=a²-2ab+b²=(a+b)²-2ab-2ab=(a+b)²-4ab=4²-4*(-6)=16+24=40

(a-b)^2=a^2-2ab+b^2=(a+b)^2 - 2ab - 2ab=(a+b)^2 - 4ab=4^2-4×(-6)=16+24=40