solve the simultaneous equations 3x+7y=18 and 7x+9y=8
3x+7y=18 (eqn 1) -multiply by 7-> 21x+49y=126 (eqn 1*)
7x+9y=8 (eqn 2) -multiply by 3-> 21x+27y=24 (eqn 2*)
(eqn 1*)-(eqn 2*) --> 22y=102 therefor y=51/11
sub in this y value back into (eqn1) --> 3x+7(51/11)=18 --> 3x+357/11=18 --> 3x=-159/11
therefore x=-53/11
RS
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