EQUATION SOLVING STRATEGIES

Question 1 :

Solve for x, y and z in the equation shown below.

(x - 2)² + (y - 3)² + (z + 4)² = 0

Answer :

In the equation (x - 2)² + (y - 3)² + (z + 4)² = 0, on the left side, we have the addition of squares of three binomials.

The square of each binomial can never be a negative value.

The only option to get zero for the addition of the squares of three binomials is that the value of square of each binomial must be zero.

Question 2 :

The equation shown above is true for all values of x ≠ 2/3, where k is a constant. What is the value of k?

Answer :

Multiply each side by (3x - 2).

kx² + 14x - 20 = (3x - 2)(5x + 8) - 4

kx² + 14x - 20 =  15x² + 24x - 10x - 4

kx² + 14x - 20 =  15x² + 14x - 4

On the both sides of the above equation, we have quadratic expressions.

If two expressions are equal, then the coefficients of like terms are also equal.

Equating the coefficients of x²,

k = 15

Question 3 :

If |1 - x| > 4 and x is positive, what is one possible value of x?

Answer :

|1 - x| > 4

1 - x > 4  or  1 - x < -4

Since x is positive, one possible value of x satisfying x > 5 is 6. That is

x = 6

Questions 4-5 refer to the following information.

An ambulance is moving at a velocity of v_a, in meters per second, towards an observer standing still on a sidewalk. Because of this movement, the actual frequency of the sound waves emitted by the ambulance's siren f_s, in hertz, is perceived by the observer to be a different frequency f_obs. The siren's sound waves travel at a velocity v_w, in meters per second. The formula above show the relationship between these variables.  

Question 4 :

Which of the following expresses the velocity of the ambulance in terms of the other variables?

Answer :

Let

a = v_a

b = v_w

c = f_s

d = f_obs

Then, the given formula becomes as shown below.

We have to find the velocity of the ambulance (v_a).

So, we have to solve for 'a'.

In the formula above, multiply both sides by (b - a).

(b - a)d = bc

bd - ad = bc

Subtract bd from both sides.

-ad = bc - bd

Multiply both sides by -1.

ad = bd - bc

Divide both sides by d.

Replace a, b and c by the original variables. 

The correct answer choice is (D).

Question 5 :

If the velocity of the siren's sound waves is 340 meters per second, the velocity of the ambulance is 22 meters per second, and the observer perceives the frequency of the siren's sound waves to be 500 hertz, which of the following is closest to the actual frequency of the siren's sound waves?

A) 468

B) 496

C) 507

D) 535

Answer :

Substitute v_w = 340, v_a = 22 and f_obs = 500. 

The correct answer choice is (A).

Question 6 :

x² + kx + 9 = (x + a)²

In the equation above, k and a are positive constants. If the equation is true for all values of x, what is the value of k?

A) 0

B) 3

C) 6

D) 9

Answer :

x² + kx + 9 = (x + a)²

Expand the right side.

x² + kx + 9 = (x + a)(x + a)

x² + kx + 9 = x² + ax + ax + a²

x² + kx + 9 = x² + 2ax + a²

Equate the coefficients of x and constant terms.

Since 'a' is a positive constant, a = 3.

Substitute a = 3 in k = 2a.

k = 2(3)

k = 6

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