✔ 最佳答案
x² + 2xy + 3y² = 2
when y = 1,
x² + 2x*1 + 3*1² = 2
x² + 2x + 1 = 0
x = -1
x² + 2xy + 3y² = 2
2x + 2( xy’ + y ) + 6y y’ = 0
2x + 2xy’ + 2y + 6yy’ = 0
when y = 1, x = -1
2(-1) + 2( -y’ + 1 ) + 6y’ = 0
-2 - 2y’ + 2 + 6y’ = 0
y’ = 0
━━━
2x + 2xy’ + 2y + 6yy’ = 0
2 + 2( xy’’ + y’ ) + 2y’ + 6( yy’’ + y’y’) = 0
2 + 2xy’’ + 2y’ + 2y’ + 6yy’’ + 6y’y’ = 0
2 + 2xy’’ + 4y’ + 6yy’’ + 6y’y’ = 0
when y = 1, x = -1, y’ = 0
2 + 2(-1)y’’ + 4(0) + 6(1)y’’ + 6(0)(0) = 0
y’’ = -½
━━━━