Algebra · real student question

Solve the system: root(2) x + root(3) y = 3 root(2) and root(3) x - root(2) y = 2 root(3).

Question

Solve the system {2x+3y=323x2y=23\begin{cases}\sqrt{2}\,x+\sqrt{3}\,y=3\sqrt{2}\\[2pt]\sqrt{3}\,x-\sqrt{2}\,y=2\sqrt{3}\end{cases}

Step-by-step solution

  1. Choose elimination over substitution. Solving either equation for a variable would drag radicals into the denominator immediately. Elimination is cleaner because the yy-coefficients 3\sqrt3 and 2-\sqrt2 multiply to the same 6\sqrt6.

  2. Scale the first equation by 2\sqrt2. 2(2x+3y)=232  2x+6y=6.\sqrt2\left(\sqrt2\,x+\sqrt3\,y\right)=\sqrt2\cdot 3\sqrt2\ \Longrightarrow\ 2x+\sqrt6\,y=6.

  3. Scale the second equation by 3\sqrt3. 3(3x2y)=323  3x6y=6.\sqrt3\left(\sqrt3\,x-\sqrt2\,y\right)=\sqrt3\cdot 2\sqrt3\ \Longrightarrow\ 3x-\sqrt6\,y=6.

  4. Add to eliminate yy. The 6y\sqrt6\,y terms cancel exactly: 5x=12  x=125.5x=12\ \Longrightarrow\ x=\frac{12}{5}.

  5. Back-substitute and rationalise. From the first original equation, 3y=321225=325  y=3253=3615=65.\sqrt3\,y=3\sqrt2-\frac{12\sqrt2}{5}=\frac{3\sqrt2}{5}\ \Longrightarrow\ y=\frac{3\sqrt2}{5\sqrt3}=\frac{3\sqrt6}{15}=\frac{\sqrt6}{5}.

  6. Check both equations numerically. With x=2.4x=2.4 and y=0.4898979y=0.4898979: the first left side is 4.2426407=324.2426407=3\sqrt2, and the second is 3.4641016=233.4641016=2\sqrt3. Both hold.

Answer

x=125,y=65x=\frac{12}{5},\qquad y=\frac{\sqrt{6}}{5}

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