1. Find the coordinates of point $P$ (the $y$-intercept of the curve).
At the y-axis, x=0.
y=5+e04=5+4=9
So, P is (0,9).
2. Find the gradient of the tangent at $P$.
y=5+4e−2x
dxdy=4(−2)e−2x=−8e−2x
At x=0, dxdy=−8e0=−8
3. Find the equation of the tangent at $P$ and the coordinates of $Q$.
Equation of tangent: y−9=−8(x−0)⟹y=−8x+9
At Q, the tangent intersects the x-axis, so y=0.
0=−8x+9⟹x=89
So, Q is (89,0).
4. Set up the integral for the area of the shaded region.
The shaded region is bounded by the curve and the tangent from x=0 to x=89.
Area = ∫089((5+4e−2x)−(−8x+9))dx
Area = ∫089(4e−2x+8x−4)dx
5. Evaluate the definite integral.
∫(4e−2x+8x−4)dx=[−24e−2x+28x2−4x]089
=[−2e−2x+4x2−4x]089
=(−2e−2(89)+4(89)2−4(89))−(−2e0+0−0)
=(−2e−49+4(6481)−29)−(−2)
=−2e−49+1681−1672+1632
=1641−2e−49
答案1641−2e−49 or 2.35 (to 3 s.f.)