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

Answered by Sophia P. Maths tutor

3259 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

Factorise 3x+12


Solve the following equation: x^2 - 11x + 18 = 0


Simplify (x + 3)(2x + 5) - (x - 1)


work out the area of a trapezium where the height is 4mm, the top length is 8mm and the bottom length is 12.5mm


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo
Cookie Preferences