document.write( "Question 634796: Hi, I've been stuck on this one for a considerable amount of time.
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document.write( "=> Show that the equation 4cos(2x)-3sin(x)csc(x)^3+6 = 0, can be expressed as
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document.write( "8y^4-10y^2+3=0 if sin(x) = y
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document.write( "Hence, solve the equation for x\r
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document.write( "Thankyou for your help \n" );
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Algebra.Com's Answer #399927 by jsmallt9(3758)![]() ![]() ![]() You can put this solution on YOUR website! \n" ); document.write( "As the problem suggest, you want everything expressed in terms of sin(x). SO we will start by substituting for the \n" ); document.write( " \n" ); document.write( "Note the use of parentheses! These are important when making substitutions. Simplifying we get: \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "Now that everything is in terms of sin(x), the next task is to get rid of the fraction. Multiplying both sides by \n" ); document.write( " \n" ); document.write( "As you may see, we're getting close. We can get the signs right if we multiply both sides by -1: \n" ); document.write( " \n" ); document.write( "And rearrange the terms: \n" ); document.write( " \n" ); document.write( "Now we can substitute \"y\" for \"sin(x)\": \n" ); document.write( " \n" ); document.write( "The reason we made this substitution is that it is easier to see how to solve \n" ); document.write( " \n" ); document.write( "than it is to see how to solve \n" ); document.write( " \n" ); document.write( "(Eventually you will see how to solve without making the substitution.) Note: An even better substitution is \n" ); document.write( " \n" ); document.write( "which I think you would agree is even easier to solve than: \n" ); document.write( " \n" ); document.write( "But we will go with the substitution your teacher/book suggested. \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "is an equation in what is called quadratic form. (A \"pure\" quadratic would have y-squared and y terms.) We can solve it with the same methods used to solve pure quadratics. One of these is factoring: \n" ); document.write( " \n" ); document.write( "If this factoring is not immediately obvious to you, then look at it for a while and let it sink in. Multiply it back out and see if you get \n" ); document.write( "Now we use the Zero Product Property: \n" ); document.write( " \n" ); document.write( "Solving these... \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "Finding the square root of each side (and not forgetting about the negative square roots) we get: \n" ); document.write( " \n" ); document.write( "Rationalizing the denominators... \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "We've solved for y. But we really want to solve for x. So it is time to substitute sin(x) back in for the y: \n" ); document.write( " \n" ); document.write( "All of these are special angle sin's so every x is a special angle (so put your calculator away). \n" ); document.write( "We should recognize that the reference angle for both \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "with the middle two equations simplifying to: \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "For \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "with the middle two equations simplifying to: \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "The full general solution to your equation is all 8 of the equations above: \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " |