FIND THE AVERAGE VALUE OF THE FUNCTION ON THE INTERVAL

For each problem, find the average value of the function over the given interval.

Problem 1 :

f(x) = 2x2 – 8x + 5; [0, 3]

Solution :

a = 0, b = 3, then b - a = 3 - 0 ==> 3

fave = 1b - a baf(x)dxfave = 13 302x2 - 8x + 5dx= 13 2x33 - 8x22 + 5x30= 132(3)33- 8(3)22 + 5(3) - 2(0)33- 8(0)22 + 5(0)= 132(27)3 - 8(9)2 + 15= 13543 - 722 + 15= 13[18 - 36 + 15]= 13[-18 + 15]= 13(-3)= -1

So, the average value of the given function in the given interval is -1.

Problem 2 :

f(x) = 5x12; [0, 1]

Solution :

a = 0, b = 1, then b - a = 1 - 0 ==> 1

fave = 1b - a baf(x)dxfave = 11 105x12dx= 105x12dx= 5 10x12dx= 5x12 + 112 + 110=5x3232 10= 5x32 × 2310= 52x33210= 10x32310=10(1)323 - 10(0)323 = 10·1323= 103= 3.333

So, the average value of the given function in the given interval is 3.34.

Problem 3 :

f(x) = - 4x - 2;[0, 1]

Solution :

a = 0, b = 1, then b - a = 1 - 0 ==> 1

fave = 1b - a baf(x)dxfave = 11 10-4x - 2dx= 10-4x - 2dx= -4 101x - 2 dx= -4 ·ln |x - 2|10= -4 ·ln |1 -2| + 4·ln |0 - 2|= -4·ln|-1| + 4·ln |-2|= -4 · ln(-(-1) + 4 ln (2))= -4 ·ln 1 + 4 · ln 2=-4 · 0 + 4 ·ln2= 4 ·ln 2

So, the average value of the given function in the given interval is 4 ln 2.

Problem 4 :

f(x) = -x + 1; [-4, 0]

Solution :

a = -4, b = 0, then b - a = 0 + 4 ==> 4

fave = 1b - a baf(x)dxfave = 14 0-4(-x + 1)dx= 14 -x22+ x0-4= 14(0)22+ 0 - -(-4)22 - 4 = 140 + 162 + 4= 14[8 + 4]= 14(12)= 3

So, the average value of the given function in the given interval is 3.

Problem 5 :

f(x) = 2x + 1; [-4, 0]

Solution :

a = -4, b = 0, then b - a = 0 + 4 ==> 4

fave = 1b - a baf(x)dxfave = 14 0-4(2x + 1)dx= 14 2x22+ x0-4= 142(0)22+ 0 - 2(-4)22 - 4 = 140 - 322 + 4= 14[-16 + 4]= 14(-12)= -3

So, the average value of the given function in the given interval is -3.

Problem 6 :

f(x) = 2x + 1; [-2, 3]

Solution :

a = -2, b = 3, then b - a = 3 + 2 ==> 5

fave = 1b - a baf(x)dxfave = 15 3-2(2x + 1)dx= 15 2x22+ x3-2= 152(3)22+ 3 - 2(-2)22 - 2 = 15182 + 3 - 82 + 2= 15[9 + 3 -4 + 2]= 15(10)= 2

So, the average value of the given function in the given interval is 2.

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