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# Basic Math/math

Question
4 over x =9 over 5 - 7x-4 divided by 5x

Hello, Kenny.

4/x = 9/5 - 7x-4/5x

Step 1: Subtract the two fractions on the right side of the equation. To do this, however, you need to find the lowest common denominator. You have 5 and 5x. The lowest common denominator for these is 5x. So, the first fraction needs to be multiplied by x, both numerator and denominator, to get a 5x on the bottom.

Result: 9x/5x.

The second fraction remains the same, because the denominator did not have to be changed. The fraction remains at 7x-4/5x.

You may now subtract, since you have common denominators.

9x-(7x-4) = 2x+4. Place this over 5x and make it equal to 4/x.

So, you now have 4/x = 2x+4/5x.

Step 2: Cross-multiply. (5x)(4) = 20x; (x)(2x+4) = 2x^2+4x.

So, you now have 2x^2 + 4x = 20x.

Step 3: Subtract 20x from both sides.

Result: 2x^2-16x = 0.

Step 4: Factor out a 2x.

Result: 2x(x-8) = 0.

Step 5: Set each 'x' factor equal to 0.

2x = 0

x-8 = 0

For 2x = 0, x must be 0 (2 x 0 = 0).

For x-8 = 0, x must be 8 (8-8 = 0).

Answer: x = 8. x cannot be 0 because the first fraction, 4/x, would then be undefined. A fraction can never have 0 as the denominator.

I hope this helps.

Regards,
John

Basic Math

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#### John Zalewski

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I can help you solve problems involving fractions, decimals, ratios, and algebra. I can teach you how to do math faster, and even in your head. I can teach math definitions, and help you study, if necessary. Please do not ask any graphing, trigonometry, or calculus questions. Try to work through homework questions before asking for assistance.

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