Algebra · real student question

Simplify (the 7th root of x squared)/((1/2)y) times (the cube root of x squared)/(the cube root of y squared) times x/(the cube root of y) times ((9/7) times the square root of y/3)/(5/x).

Question

Simplify x2712y×x23y23×xy3×97y35x.\frac{\sqrt[7]{x^2}}{\tfrac12 y}\times\frac{\sqrt[3]{x^2}}{\sqrt[3]{y^2}}\times\frac{x}{\sqrt[3]{y}}\times\frac{\tfrac97\sqrt{\tfrac{y}{3}}}{\tfrac5x}.

Step-by-step solution

  1. Convert every radical to a fractional exponent. Using amn=am/n\sqrt[n]{a^m}=a^{m/n}: x27=x2/7\sqrt[7]{x^2}=x^{2/7}, x23=x2/3\sqrt[3]{x^2}=x^{2/3}, y23=y2/3\sqrt[3]{y^2}=y^{2/3}, y3=y1/3\sqrt[3]{y}=y^{1/3}, and y3=y1/23\sqrt{\tfrac y3}=\tfrac{y^{1/2}}{\sqrt3}. Exponent form is the only practical way to combine roots of different orders.

  2. Clear the fractional coefficients inside the fractions. Dividing by 12y\tfrac12 y means multiplying by 2y\tfrac{2}{y}, and dividing by 5x\tfrac5x means multiplying by x5\tfrac x5: 2x2/7y×x2/3y2/3×xy1/3×9x35y1/23.\frac{2x^{2/7}}{y}\times\frac{x^{2/3}}{y^{2/3}}\times\frac{x}{y^{1/3}}\times\frac{9x}{35}\cdot\frac{y^{1/2}}{\sqrt3}. Note the fourth factor contributes an extra xx, which is easy to miss.

  3. Gather the numerical coefficients. 2×935=18352\times\tfrac{9}{35} = \tfrac{18}{35}, and the 13\tfrac{1}{\sqrt3} stays for now: the constant is 18353\dfrac{18}{35\sqrt3}.

  4. Add the exponents of x. The powers present are x2/7x^{2/7}, x2/3x^{2/3}, x1x^1 (third factor) and x1x^1 (from the fourth): 27+23+1+1=621+1421+4221=6221.\frac27+\frac23+1+1 = \frac{6}{21}+\frac{14}{21}+\frac{42}{21} = \frac{62}{21}.

  5. Add the exponents of y. The numerator supplies y1/2y^{1/2}; the denominators supply y1y2/3y1/3=y2y^{1}\cdot y^{2/3}\cdot y^{1/3} = y^{2}. Hence y1/22=y3/2=1y3/2.y^{1/2-2} = y^{-3/2} = \frac{1}{y^{3/2}}.

  6. Rationalise and reduce the constant. 18353=183105=6335\dfrac{18}{35\sqrt3} = \dfrac{18\sqrt3}{105} = \dfrac{6\sqrt3}{35}, so expression=63x62/2135y3/2.\text{expression} = \frac{6\sqrt3\,x^{62/21}}{35\,y^{3/2}}.

  7. Check numerically. At x=2x=2, y=3y=3 the original product evaluates to 0.442300240.44230024, and 63262/213533/2=0.44230024\dfrac{6\sqrt3\cdot 2^{62/21}}{35\cdot 3^{3/2}} = 0.44230024 - identical to eight decimals.

Answer

63x62/2135y3/2\frac{6\sqrt{3}\,x^{62/21}}{35\,y^{3/2}}

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