document.write( "Question 1478: the triangle with sides of 5,8,9, is acute, right or obtuse \n" ); document.write( "

Algebra.Com's Answer #525 by khwang(438) $\"\"$ $\"About$

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Among 5,8 & 9 , the largest is 9 side. Let the angle opposite to the side 9
\n" ); document.write( " is A which is also the largest angle . By the cosine law:
\n" ); document.write( " 9^2 = 5^2 + 8^2 - 2*5*8 cos A = 25 + 64 - 80 cos A = 89 - 80 cos A
\n" ); document.write( " So, cos A = 8/80 =1/10 > 0.
\n" ); document.write( " Hence, A is acute and the triangle is acute.\r
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