AP Calculus AB Exam Question:
Find the limit algebraically:
x→2πlimsin2(2x−2)cos(x−1)Step-by-Step Solution:
To find the limit as x approaches 2π, we can use algebraic techniques such as factoring and simplifying.
Let's start by simplifying the expression:
x→2πlimsin2(2x−2)cos(x−1)Recall the identity cos(x−1)=cos(x)cos(1)+sin(x)sin(1). Using this, the expression becomes:
x→2πlimsin2(2x−2)cos(x)cos(1)+sin(x)sin(1)Next, observe the denominator sin2(2x−2). We know that sin(2θ)=2sin(θ)cos(θ). Applying this identity, we have:
x→2πlim(2sin(x−1)cos(x−1))2cos(x)cos(1)+sin(x)sin(1)Simplifying further, we get:
x→2πlim4sin2(x−1)cos2(x−1)cos(x)cos(1)+sin(x)sin(1)Now, we need to analyze the numerator and the denominator separately.
Let's evaluate the numerator first. For the limit as x approaches 2π:
x→2πlimcos(x)cos(1)+sin(x)sin(1)Using the limit properties, we can evaluate each term separately. Recall that limx→2πcos(x)=0 and limx→2πsin(x)=1. Plugging these values into the expression, we get:
0⋅cos(1)+1⋅sin(1)=sin(1)Next, let's evaluate the denominator. For the limit as x approaches 2π:
x→2πlim4sin2(x−1)cos2(x−1)Using the limit properties, we can evaluate each term separately. Recall that limx→2πcos(x−1)=0 and limx→2πsin(x−1)=1. Plugging these values into the expression, we get:
4⋅(1)2⋅(0)2=0Finally, we can put the evaluated numerator and denominator together to find the overall limit.
x→2πlim4sin2(x−1)cos2(x−1)cos(x)cos(1)+sin(x)sin(1)=0sin(1)However, since the denominator evaluated to zero, we need to further analyze the behavior around 2π. For this, we can examine the behavior of the original numerator and denominator.
Looking at the original expression, we know that sin2(2x−2) approaches zero as x approaches 2π, while cos(x−1) does not. Therefore, the limit of the expression does not exist algebraically as it is undefined.
Hence, the final answer is:
x→2πlimsin2(2x−2)cos(x−1) is undefined.