x 2 − 3 ∣ x ∣ + 2 = 0
Find the number of real solutions of the equation above.
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how is 4 the answer?
First, this problem is too overrated :D
Second, we divide this equation into 2 cases:
Case 1: If x ≥ 0 ⇔ ∣ x ∣ = x ⇔ x 2 − 3 x + 2 = 0 ⇔ x ∈ { 1 ; 2 } , which gives us 2 solutions of x
Case 2: If x < 0 ⇔ ∣ x ∣ = − x ⇔ x 2 + 3 x + 2 = 0 ⇔ x ∈ { − 1 ; − 2 } , which gives us another 2 solutions of x
In total, there are 2 + 2 = 4 solutions of x satisfy the equations.
Though this is a relatively small matter, shouldn't x=0 be included in some part of the domain, as the function is defined there ?
i.e. Case 1 : x ≥ 0 etc
Case 2 : x < 0 ... etc
But aside from that technicality, I did it exactly the same way ^^
Number of reals solutions will be 4 because it is mod x
So there will be two equations
so number of real solutions comes out to be 4
Notice that the function is even: we can restrict our study to x 2 − 3 x + 2 = ( x − 2 ) ⋅ ( x − 1 ) which has two positive roots. By simmetry (with respect to the y axis), we can conclude that the number of solutions of the starting equation is therefore 2 ⋅ 2 = 4 .
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x 2 = ∣ x ∣ 2
∣ x ∣ = p
p 2 − 3 p + 2 = 0 ⇒ ( p − 2 ) ( p − 1 ) = 0 ⇒ p = 1 , 2
∣ x ∣ = 1 , 2 ⇒ x = ± 1 , ± 2