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12. Find the solution set of (x-1) (x+2)>4. Graph your answer.

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Sagot :

Answer:

Well, we have to see for three cases- i. x<1 , ii. 1<x<2 and iii. x>2 .

We need not consider 1 and 2 since we can see that the equation is not satisfied for x=1 or x=2 .

Case i.

x<1āŸ¹xāˆ’1<0āŸ¹|xāˆ’1|=āˆ’(xāˆ’1)=1āˆ’x and |xāˆ’2|=āˆ’(xāˆ’2)=2āˆ’x ( āˆµx<1,āˆ“x<2 and xāˆ’2<0 )

So here we get the equation as 1āˆ’x+2ā€“x=4 , which gives 2x=āˆ’1.

āˆ“x=āˆ’12=āˆ’0.5 .

What is the solution of |x-1|+|x-2|ā‰„4?

Well, we have to see for three cases- i. x<1 , ii. 1<x<2 and iii. x>2 .

We need not consider 1 and 2 since we can see that the equation is not satisfied for x=1 or x=2 .

Case i.

x<1āŸ¹xāˆ’1<0āŸ¹|xāˆ’1|=āˆ’(xāˆ’1)=1āˆ’x and |xāˆ’2|=āˆ’(xāˆ’2)=2āˆ’x ( āˆµx<1,āˆ“x<2 and xāˆ’2<0 )

So here we get the equation as 1āˆ’x+2ā€“x=4 , which gives 2x=āˆ’1.

āˆ“x=āˆ’12=āˆ’0.5 .

Case ii.

1<x<2āŸ¹xāˆ’1>0 but xāˆ’2<0 . āˆ“|xāˆ’1|=xāˆ’1 and |xāˆ’2|=2āˆ’x

So here we get the equation as xāˆ’1+2āˆ’x=4āŸ¹1=4 which is not possible.

Hence we do not have any solution for the equation in the interval (1,2) .

Case iii.

x>2āŸ¹x>1 . Hence xāˆ’1>0 and xāˆ’2>0 .

āˆ“|xāˆ’1|=xāˆ’1 and |xāˆ’2|=xāˆ’2

So the equation becomes xāˆ’1+xāˆ’2=4 , which gives 2x=7 .

āˆ“x=72=3.5 .

Hence we get two solutions for the given equation:

x=āˆ’12 and x=72

Why did we divide the domain (i.e. the set of real numbers) into three such parts?

If we want to define f(x)=|xāˆ’1|+|xāˆ’2| without using modulus symbols we would have to do it in the following way.

In other words, f(x) is not differentiable at x=1 and x=2 .

Step-by-step explanation:

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