Given, 2x−y=4......(i)(a,b) lies on line 2x−y−4=0
b=2a−4 (‌
−4m−n
m+n
)=2(‌
m+2n
m+n
)−4 −4m−n=2m+4n−4m−4n 2m+n=0‌end‌gathered or n=−2m Equation of line joining the points (2,−1) and (1,−4) is ‌y+4=(‌
−1+4
2−1
)(x−1) ‌y+4=3(x−1) ‌y+4=3x−3 ‌3x−y=7......(ii) Subtracting Eq. (i) from Eq. (ii), we get ‌x=3‌ and ‌y=2 ‌∴a=3,b=2 ‌‌ So, ‌4(a−b(‌