How do you solve the system 7r-2s=33 and 2r+7s=70?

1 Answer
Don't Memorise
Aug 22, 2015

The solutions are
color(blue)(s=8,r=7

Explanation:

7r-2s=33 , multiplying by 2
color(blue)(14r)-4s=66 .....equation 1

2r+7s=70, multiplying by 7
color(blue)( 14r)+49s=490.....equation 2

Solving by elimination
Subtracting equation 2 from 1
color(blue)(14r)-4s=66
cancelcolor(blue)( -14r)-49s=-490

-53s=-424
color(blue)(s=8

Finding r from equation 1
7r-2s=33
7r=33+2s
7r=33+16
7r=49
color(blue)(r=7

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