solve-x-3-7x-2-7-x-15-lt-0-

Question Number 79279 by jagoll last updated on 24/Jan/20

solve

∣ x ∣^{3} - {7 x}^{2} + 7 ∣ x ∣ + 15 < 0

Commented by jagoll last updated on 24/Jan/20

thanks

Commented by MJS last updated on 24/Jan/20

sorry but {it}^{'} s wrong

Commented by john santu last updated on 24/Jan/20

w h e r e i s w r o n g ?

Commented by MJS last updated on 24/Jan/20

you should plot the function or scetch it

Answered by MJS last updated on 24/Jan/20

case 1 x ⩾ 0

x^{3} - 7 x^{2} + 7 x + 15 = 0

\Rightarrow x = - 1 \lor x = 3 \lor x = 5

testing x = 4 : 4^{3} - 7 \times 4^{2} + 7 \times 4 + 15 = - 5

case 2 x < 0

- x^{3} - 7 x^{2} - 7 x + 15 = 0

\Rightarrow x = - 5 \lor x = - 3 \lor x = 1

testing x = - 4 : - {(- 4)}^{3} - 7 \times {(- 4)}^{2} - 7 \times 4 + 15 = - 5

\Rightarrow

- 5 < x < - 3 \lor 3 < x < 5

or

3 <∣ x ∣< 5

Commented by john santu last updated on 24/Jan/20

y o u r a r e r i g h t . i^{'} m f o r g o t

t h e d e f i n i t i o n s i g n (x)

Commented by jagoll last updated on 24/Jan/20

thanks you sir

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