A curve passes through the point (0, 2), and the slope of the tangent to the curve at any point (x, y) on it is \(y + 2x\). The y-coordinate of the point on the curve where \(x = 1\) is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(4e - 4\)
The slope of the tangent is \(\frac{dy}{dx}\), so
\( \displaystyle \frac{dy}{dx} = y + 2x \)
\( \displaystyle \frac{dy}{dx} - y = 2x \)
This is a linear equation with \(P = -1\), so the integrating factor is \(e^{-x}\):
\( \displaystyle y\,e^{-x} = \int 2x\,e^{-x}\,dx \)
Integrating by parts:
\( \displaystyle \int 2x\,e^{-x}\,dx = -2x\,e^{-x} - 2e^{-x} + C \)
So
\( y = -2x - 2 + Ce^{x} \)
The curve passes through (0, 2):
\( 2 = -2 + C \Rightarrow C = 4 \)
So \(y = 4e^x - 2x - 2\), and at \(x = 1\):
\( y = 4e - 2 - 2 = 4e - 4 \)