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Right Riemann sum for f(x) = e^x on [0,2] with n = 4

Consider the function f(x)=exf(x) = e^x on the interval [0,2][0, 2].

Partition [0,2][0, 2] into n=4n = 4 equal subintervals and use the right endpoint of each subinterval to approximate the area under f(x)=exf(x) = e^x on [0,2][0,2].

What is the value of the right Riemann sum R4R_4?

Hint

First find Δx=b−an\Delta x = \frac{b-a}{n} and list the right endpoints x1,x2,x3,x4x_1, x_2, x_3, x_4. Then compute R4=Δx[f(x1)+f(x2)+f(x3)+f(x4)]R_4 = \Delta x \left[f(x_1) + f(x_2) + f(x_3) + f(x_4)\right].

Step-by-step solution

Since a=0a=0, b=2b=2, and n=4n=4, the width of each subinterval is Δx=2−04=0.5\Delta x = \frac{2-0}{4} = 0.5. The subintervals are [0,0.5],[0.5,1],[1,1.5],[1.5,2][0,0.5], [0.5,1], [1,1.5], [1.5,2], so the right endpoints are x1=0.5x_1 = 0.5, x2=1x_2 = 1, x3=1.5x_3 = 1.5, and x4=2x_4 = 2.

The right Riemann sum is R4=Δx[f(0.5)+f(1)+f(1.5)+f(2)]=0.5[e0.5+e1+e1.5+e2]R_4 = \Delta x \left[f(0.5) + f(1) + f(1.5) + f(2)\right] = 0.5\left[e^{0.5} + e^{1} + e^{1.5} + e^{2}\right]. Evaluating, e0.5≈1.6487e^{0.5} \approx 1.6487, e1≈2.7183e^{1} \approx 2.7183, e1.5≈4.4817e^{1.5} \approx 4.4817, and e2≈7.3891e^{2} \approx 7.3891, so R4≈0.5(16.2378)≈8.1189R_4 \approx 0.5(16.2378) \approx 8.1189.

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