Core Connections Algebra 2, 2013
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Core Connections Algebra 2, 2013 View details
1. Section 7.1
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Exercise 8 Page 316

Rearrange the radical equation so that one of the radical expressions is isolated. Then, raise both sides of the equation to a power equal to the index of the radicals.

x=5

Practice makes perfect

To solve equations with a variable expression inside a radical, we will first rearrange the radical equation so that one of the radical expressions is isolated. Then we can raise both sides of the equation to a power equal to the index of the radicals.

2sqrt(21-x)-sqrt(3x-6)=5
2sqrt(21-x)=5+sqrt(3x-6)
â–¼
LHS^2=RHS^2
(2sqrt(21-x))^2=(5+sqrt(3x-6))^2
4(sqrt(21-x))^2=(5+sqrt(3x-6))^2
4(21-x)=(5+sqrt(3x-6))^2

To continue simplifying the right-hand side of the equation, we can expand the squared binomial using the format of a perfect square trinomial.

4(21-x)=(5+sqrt(3x-6))^2
â–¼
(a+b)^2=a^2+2ab+b^2
4(21-x)=5^2+2(5)sqrt(3x-6)+(sqrt(3x-6))^2
4(21-x)=25+2(5)sqrt(3x-6)+(sqrt(3x-6))^2
4(21-x)=25+10sqrt(3x-6)+(sqrt(3x-6))^2
4(21-x)=25+10sqrt(3x-6)+(3x-6)
4(21-x)=25+10sqrt(3x-6)+3x-6
4(21-x)=3x+19+10sqrt(3x-6)

Now that we have expanded and fully simplified the right-hand side, we can continue solving for x using the Properties of Equality.

4(21-x)=3x+19+10sqrt(3x-6)
84-4x=3x+19+10sqrt(3x-6)
84-7x=19+10sqrt(3x-6)
65-7x=10sqrt(3x-6)

Since we still have a radical expression on one side of the equation, we will follow the same method as before — we will raise both sides of the equation to the second power. When we do this, we will have to expand the left-hand side of the equation using a perfect square trinomial.

65-7x=10sqrt(3x-6)
(65-7x)^2=(10sqrt(3x-6))^2
â–¼
(a-b)^2=a^2-2ab+b^2
65^2-2(65)(7x)+(7x)^2=(10sqrt(3x-6))^2
4225-2(65)(7x)+49x^2=(10sqrt(3x-6))^2
4225-910x+49x^2=(10sqrt(3x-6))^2
4225-910x+49x^2=100(sqrt(3x-6))^2
4225-910x+49x^2=100(3x-6)

Finally, all of the radicals have been removed from the equation. Because we have an x-variable with an exponent, we cannot directly solve for it. Therefore, let's move all of the non-zero terms to the left-hand side of the equation and see what remains.

4225-910x+49x^2=100(3x-6)
â–¼
Rearrange equation
4225-910x+49x^2=300x-600
4225-1210x+49x^2=-600
4825-1210x+49x^2=0

We are left with a quadratic equation. We can solve it using the Quadratic Formula. ax^2+ bx+ c=0 ⇕ x=- b± sqrt(b^2-4 a c)/2 a Let's identify the values of a, b, and c in our case. 4825-1210x+49x^2=0 ⇓ 49x^2+( -1210)x+ 4825=0 We can see that a= 49, b= - 1210, and c= 4825. Let's substitute these values into the Quadratic Formula.

x=- b±sqrt(b^2-4ac)/2a
x=- ( -1210)±sqrt(( - 1210)^2-4( 49)( 4825))/2( 49)
â–¼
Solve for x and Simplify
x=1210±sqrt((-1210)^2-4(49)(4825))/2(49)
x=1210±sqrt(1464100-4(49)(4825))/2(49)
x=1210±sqrt(1464100-975700)/98
x=1210±sqrt(518400)/98
x=1210±720/98
x=2(605± 360)/98
x=605± 360/49

The solutions for this equation are x= 605± 36049.

x=605± 360/49
x_1=605-360/49 x_2=605+360/49
x_1=245/49 x_2=965/49
x_1=5 x_2=965/49

Using the Quadratic Formula, we found that the solutions of the given equation are x_1=5 and x_2= 96549. Let's check them to see if we have any extraneous solutions.

2sqrt(21-x)-sqrt(3x-6)? =5
2sqrt(21- 5)-sqrt(3( 5)-6)? =5
â–¼
Simplify left-hand side
2sqrt(21-5)-sqrt(15-6)? =5
2sqrt(16)-sqrt(9)? =5
2(4)-3? =5
8-3? =5
5=5

Substitution resulted in a true statement, so x=5 is a correct solution. Let's check 96549.

2sqrt(21-x)-sqrt(3x-6)? =5
2sqrt(21- 965/49)-sqrt(3( 965/49)-6)? =5
â–¼
Simplify left-hand side
2sqrt(21-965/49)-sqrt(2895/49-6)? =5
2sqrt(1029/49-965/49)-sqrt(2895/49-294/49)? =5
2sqrt(64/49)-sqrt(2601/49)? =5
2(8/7)-51/7? =5
16/7-51/7? =5
-35/7? =5
-5≠5

The substitution of 96549 resulted in a contradiction. This means that 96549 is an extraneous solution. Therefore, x=5 is the only real solution to the equation.