Big Ideas Math Algebra 1, 2015
BI
Big Ideas Math Algebra 1, 2015 View details
Cumulative Assessment

Exercise 2 Page 98

Practice makes perfect
a Consider the given inequality.
ax+4≤ 3x+b We are given that a=5. Let's substitute this value into the inequality and solve it for x.
ax+4 ≤ 3x+b
5x+4 ≤ 3x+b
Solve for x
2x+4 ≤ b
2x ≤ b-4
x ≤ b-4/2
Since we want the solution to be less than -3, the right-hand side of the inequality has to equal -3. b-4/2=-3 Let's solve this equation for b.
b-4/2=-3
b-4=-6
b=-2
When a=5 and b=-2, x≤ -3. Now we can complete the statement.

When a=5 and b=-2, x≤-3.

b Since we want the solution of the inequality to be all real numbers, we have to eliminate x from the inequality and obtain an statement that is always true. This can be done if we have the same x-terms on both sides of the inequality.
ax+4≤ 3x+b Since we have 3x on the right-hand side, we will substitute a= 3.
ax+4 ≤ 3x+b
3x+4 ≤ 3x+b
4 ≤ b
If we want 4 ≤ b to be always true, we can substitute any number for b that makes this inequality true. Let's choose b= 5. 4 ≤ 5 This statement is always true and the solution to the original inequality will be all real numbers. Now we can complete the statement.

When a=3 and b=5, the solution of the inequality is all real numbers.

c Since we want the inequality to have no solution, we have to eliminate x from the inequality and obtain an statement that is always false. We found in Part B that we can eliminate x if we let a=3.
ax+4 ≤ 3x+b
3x+4 ≤ 3x+b
4 ≤ b

If we want 4 ≤ b to be a contradiction, we have to substitute a number for b that makes this inequality false. Let's choose b= 3. 4 ≰ 3 This is always false and the original inequality will have no solution. Therefore, when a=3 and b=3, the inequality has no solution. Now we can complete the statement.

When a=3 and b=3, the inequality has no solution.