Solve the simultaneous equations: 5x+y=21, x-3y=9

Step 1. Take one equation and make either x or y the subject of the formulax=9+3y, 5x+y=21Step 2. Substitute in the equation5(9+3y)+y=21Step 3. Make y the subject of the formula45+15y+y=21 (multiplied out the brackets)16y=-24 (Subtracted 45 from both sides)y=-24/16 (Divided by 16 on both sides)y=-3/2 (Scaled the fraction down) Step 4. Find out what x is equal tox=9+3(-3/2)x=4.5 or 9/2

MJ
Answered by marcus J. Maths tutor

2717 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

What is the area of triangle ABC where AB = 5 cm, BC = 12 cm and angle ABC = 50 degrees?


The diagram shows the position of two ships, A and B, and a lighthouse L. Ship A is 5km from L on a bearing of 070° from L. Ship B is 3km from L on a bearing of 210° from L. Find the distance between A and B correct to 3.s.f.


How can you differentiate when to use SohCahToa and when to use the sine/cosine rules?


Make x the subject of, 4(x+1)/(x+2) = y


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