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Mashcka [7]
3 years ago
10

Find the value of a for which the solution of the inequality is all real numbers.

Mathematics
1 answer:
Liono4ka [1.6K]3 years ago
4 0

Answer:

a=3,\text{ then } x\in(-\infty,\infty)\\ \\a\in(-\infty,3),\text{ then }x\in \left[\dfrac{-4a-8}{3-a},\infty\right)\\ \\a\in(3,\infty),\text{ then }x\in \left(-\infty, \dfrac{-4a-8}{3-a}\right]

Step-by-step explanation:

In the inequality

3x+8+2ax\ge 3ax-4a\ \ \ (1)

a is an arbitrary real number.

Separate the terms with x into left side and the terms without x in the right side:

3x+2ax-3ax\ge -4a-8\\ \\3x-ax\ge -4a-8\\ \\(3-a)x\ge -4a-8\ \ \ (2)

First, look at the leading coefficient at x. If this coefficient is equal to 0 (when a=3), then the inequality is

0\ge -4a-8\\ \\0\ge -12-8\ [\text{Substituted }a=3]\\ \\0\ge -20

This is true inequality for all x, so at a=3, the inequality (1) has the solution x\in (-\infty,\infty)

Now, if the leading coefficient

3-a>0\\ \\a

then we can divide the inequality (2) by this positive number 3-a and get

x\ge \dfrac{-4a-8}{3-a}

If the leading coefficient

3-a3,

then we can divide the inequality (2) by this negative number 3-a and get

x\le \dfrac{-4a-8}{3-a}

So, the answer is

a=3,\text{ then } x\in(-\infty,\infty)\\ \\a\in(-\infty,3),\text{ then }x\in \left[\dfrac{-4a-8}{3-a},\infty\right)\\ \\a\in(3,\infty),\text{ then }x\in \left(-\infty, \dfrac{-4a-8}{3-a}\right]

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