Solve the simultaneous equations: 5x + y = 21, x - 3y = 9
5x + y = 21x - 3y = 9First, find the lowest common multiple for x or y and make the equations equal for either x or y.Here, we multiply the second equation by 5 to make the amount of x the same. The equations become:5x + y = 215x - 15y = 45Then subtract one from the other to eradicate x.y - - 15 y = 16y and 21 - 45 = -2416y = -24Solve for y.y = -24/16 (both divisible by 8) so y = -3/2 or -1.5Insert y into either of the original equations.x - (-3*3/2) = 9x + 9/2 = 9 x = 9 - 9/2 x = 18/2 - 9/2 x = 9/2 or 4.5So: x = 4.5 y = -1.5
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