document.write( "Question 1114003: Triangle ABC has AB= 7 cm, AC = 13, BC = x cm and angle ABC = 60 degrees. Calaculate the exact value of x \n" ); document.write( "

Algebra.Com's Answer #729013 by rothauserc(4718) $\"\"$ $\"About$

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use the law of cosines
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\n" ); document.write( "13^2 = 7^2 +x^2 - 7 * x * cos(60)
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\n" ); document.write( "169 = 49 +x^2 - 7x * (1/2)
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\n" ); document.write( "x^2 -3.5x -120 = 0
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\n" ); document.write( "use the quadratic formula
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\n" ); document.write( "x = (-(-3.5) +square root((-3.5)^2-4*1*(-120))) / (2 * 1) = 12.8434
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\n" ); document.write( "x = (-(-3.5) -square root((-3.5)^2-4*1*(-120))) / (2 * 1) = −9.3434
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\n" ); document.write( "reject negative value for x
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\n" ); document.write( "x = 12.8434 cm
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