Question 167729
Simultaneous equation 
3x-4y=5
3x^2-xy-3y^2=21
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Solve the 1 eqn for y
3x-4y=5
-4y = 5-3x
y = (3/4)x - 5/4
Sub for y into the 2nd eqn
3x^2 - x*((3/4)x - 5/4) - 3*((3/4)x - 5/4)^2 = 21
Now it's all in x
3x^2 - (3/4)x^2 + 5x/4 - 3*((9/16)x^2 - 15x/8 + 25/16 = 21
Multiply by 16
48x^2 - 12x^2 + 20x - 27x^2 + 90x - 75 = 336
9x^2 + 110x - 261 = 0
*[invoke solve_quadratic_equation 9,110,-411]
x = 3, y = 1
x = -15 2/9, y = -38/3