Question

solve this equation 90=n/2[2×2+(n-1)]

Answer 1

90=n/2{4+n-1}

90=n/2{n+3}

90×2=n^2+3n

n^2+3n-180=0

n^2+15n-12n-180=0

;n(n+15)-12(n+15)=0

;(n+15)(n-12)=0

;n=12,-15