Question 971394
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B=base; H=height (altitude)=B-3cm; A=area=90cm^2
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{{{(1/2)BH=A}}} Substitute for H.
{{{(1/2)B(B-3cm)=90cm^2}}} Multiply each side by 2.
{{{B^2-3B=180cm^2}}} Subtract 180cm^2 from each side.
{{{B^2-3B-180=0}}}
{{{(B-15)(B+12)=0}}}
{{{B-15=0}}} {{{or}}} {{{B+12=0}}}
{{{B=15}}} {{{or}}} {{{B=-12}}}
ANSWER 1: The base is 15 centimeters.
{{{H=B-3cm}}}
{{{H=15cm-3cm}}}
{{{H=12 cm}}}
ANSWER 2: The height (altitude) is 12 centimeters.