document.write( "Question 473019: In triangle ABC, angle B is an obtuse angle, AB=15, BC=20, and the area of the triangle is 90. What is the measure of angle B?\r
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Algebra.Com's Answer #324336 by ccs2011(207) $\"\"$ $\"About$

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Area = (1/2)*base*height
\n" ); document.write( "Let BC be the base of the triangle, Area is 90, h is height
\n" ); document.write( " $\"90+=+%281%2F2%29%2A20%2Ah\"$
\n" ); document.write( " $\"90+=+10h\"$
\n" ); document.write( " $\"9+=+h\"$
\n" ); document.write( "Now imagine a perpendicular line drawn straight down from A, call it point D
\n" ); document.write( "Then ADB makes a right triangle, where the hypotenuse is AB and one leg is h.
\n" ); document.write( "Now find angle ABD which is the supplement to angle B.
\n" ); document.write( "Using trig relationship: Sin = opp/hyp
\n" ); document.write( " $\"sin%28ABD%29=+9%2F15\"$
\n" ); document.write( " $\"ABD+=+sin%5E-1%289%2F15%29+=+36.87\"$
\n" ); document.write( "Angle B = 180 - ABD
\n" ); document.write( " $\"B+=+180+-+36.87+=+143.13\"$
\n" ); document.write( "Therefore measure of angle B is 143.13 degrees.\r
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