−ab.....(i) Also, (1,−1) is a point on H=0 a+1+b=0⇒a=−(b+1) Substitute value of a in Eq. (i), 5|−1|=√‌
1
4
+(b+1)b ⇒25=4(‌
1
4
+b2+b)⇒25=1+4b2+4b ⇒4b2+4b−24=0⇒b2+b−6=0 ⇒b2+3b−2b−6=0⇒b=2,−3 ⇒‌‌b2+3b−2b−6=0⇒b=2,−3 If b=2, then a=−3 - If b=−3, then a=2 a2+ab+b2=4−6+9=7