Question

3x+4y=13, xy=1, find 3x-4y

Answer 1

Answer:

Step-by-step explanation:

x=1/y

3x+4y=13

3/y+4y=13

3+4y²=13y

4y²-13y+3=0

4y²-12y-y+3=0

4y(y-3)-1(y-3)=0

(4y-1)(y-3)=0

y=3,1/4

x=1/3,4

Case 1st=> x=1/3,y=3

3x-4y=1-12=(-11)

Case 2nd=> x=4,y=1/4

3x-4y=12-1=11