Question 173140
Let base  = {{{b}}}
height = {{{b + 8}}}
{{{90 = (1/2)*b*(b + 8)}}}
multiply both sides buy {{{2}}}
{{{180 = b^2 + 8b}}}
Complete the square
{{{b^2 + 8b + (8/2)^2 = 180 + (8/2)^2}}}
{{{(b + 4)^2 = 196}}}
take square root of both sides
{{{b + 4 = 14}}}
{{{b = 10}}}
{{{b + 8 = 18}}}
The base is 10 cm and the height is 18 cm
check:
{{{90 = (1/2)*b*h}}}
{{{90 = (1/2)*10*18}}}
{{{90 = 180/2}}}
{{{90 = 90}}}
OK