document.write( "Question 1089267: if tan a and tan b are the roots of equation 4x^2-7x+1=0 then evaluate 4sin^2(a+b)-7sin(a+b)cos(A+B)+cos^2(A+B) \n" ); document.write( "
Algebra.Com's Answer #703616 by ikleyn(52909)\"\" \"About 
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\n" ); document.write( "if tan a and tan b are the roots of equation 4x^2-7x+1=0 then evaluate 4sin^2(a+b)-7sin(a+b)cos(A+B)+cos^2(A+B)
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document.write( "if tan(a) and tan(b) are the roots of equation 4x^2-7x+1=0 then\r\n" );
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document.write( "    tan(a) + tan(b) = \"7%2F4\"  and  tan(a)*tan(b) = \"1%2F4\",    (1)\r\n" );
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document.write( "according to Vieta's formulas/theorem.\r\n" );
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document.write( "It implies  tan(a+b) = \"%28tan%28a%29+%2B+tan%28b%29%29%2F%281-+tan%28a%29%2Atan%28b%29%29\" = \"%28%287%2F4%29%29%2F%281-1%2F4%29\" = \"%28%287%2F4%29%29%2F%28%283%2F4%29%29\" = \"7%2F3\"  and then  \"cos%5E2%28a%2Bb%29\" = \"1%2F%281%2Btan%5E2%28a%2Bb%29%29\" = \"1%2F%281+%2B+%287%2F3%29%5E2%29\" = \"1%2F%281+%2B+49%2F9%29\" = \"9%2F%289+%2B+49%29\" = \"9%2F58\".       (2)\r\n" );
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document.write( "Then  \r\n" );
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document.write( "  \"4sin%5E2%28a%2Bb%29-7sin%28a%2Bb%29cos%28a%2Bb%29%2Bcos%5E2%28a%2Bb%29\" = \"cos%5E2%28a%2Bb%29%2A%284%2Atan%5E2%28a%2Bb%29+-7%2Atan%28a%2Bb%29+%2B1%29\" = \"cos%5E2%28a%2Bb%29%2A%284%2A%287%2F3%29%5E2+-+7%2A%287%2F3%29+%2B+1%29\" = \"cos%5E2%28a%2Bb%29%2A%284%2A49%2F9+-+7%2A%287%2F3%29+%2B+1%29\" = \r\n" );
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document.write( "= \"cos%5E2%28a%2Bb%29%2A%28%284%2A49%29%2F9+-+%287%2A7%2A3%29%2F9+%2B+9%2F9%29\" = \"cos%5E2%28a%2Bb%29%2A%28%284%2A49-7%2A7%2A3%2B9%29%2F9%29\" = \"cos%5E2%28a%2Bb%29%2A%2858%2F9%29\".\r\n" );
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document.write( "Substitute here  \"cos%5E2%28a%2Bb%29\" = \"9%2F58\"  from (2),  and you will get\r\n" );
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document.write( "\"4sin%5E2%28a%2Bb%29-7sin%28a%2Bb%29cos%28a%2Bb%29%2Bcos%5E2%28a%2Bb%29\" = . . . = \"%289%2F58%29%2A%2858%2F9%29\" = 1.\r\n" );
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\n" ); document.write( "\n" ); document.write( "Answer. The value under the question is 1.\r
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