Question 969876
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The diagonal is the hypotenuse of a right triangle with height and width as legs, so:
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Let c=diagonal=35 in, a=height=21 in, b=width
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{{{a^2+b^2=c^2}}} Subtract a^2 from each side.
{{{b^2=c^2-a^2}}} Find the square root of each side.
{{{b=sqrt(c^2-a^2)}}} Plug in values.
{{{b=sqrt((35in)^2-(21in)^2)}}}
{{{b=sqrt(1225in^2-441in^2)}}}
{{{b=sqrt(784in^2)}}}
{{{b=28in}}}
ANSWER: The width is 28 inches.