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

SP
Answered by Sophia P. Maths tutor

3720 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

Find the length of the hypotenuse if the right angled triangle's other two sides are of length 5cm and 12cm.


Find the equation of the straight line which passes through the point (0, 3) and is perpendicular to the straight line with equation y = 2x.


4x+9y=59.5 and x+y=8. Find the values of x and y.


Solve the following ((3x + 1)/2x ) = 4


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences