find the domain of..

f(x) = log7 log 5 log3 log2 (2x3 + 5x2 - 14x)

9 Answers

1
ANKIT MAHATO ·

yeh kaisa atyachar .. so many bases !!

106
Asish Mahapatra ·

log5log3log2(2x3+5x2-14x) > 0
==> log3log2(2x3+5x2-14x) > 1
==> log2(2x3+5x2-14x) > 3
==> (2x3+5x2-14x) > 23
==> 2x3+5x2-14x - 8 > 0
==> x=2 is a solution by inspection

So, 2x3+5x2-14x - 8 = (x-2)(2x2+9x+4)
= (x-2)(2x+1)(x+4)

So, x = (-4,-1/2) U (2,∞)

1
The Race begins... ·

log 5 log3 log2 (2x3+5x2-14x) > 0

=> log3 log2 (2x3+5x2-14x) > 1

=> log2 (2x3+5x2-14x) > 3

=> 2x3+5x2-14x > 8

=> 2x3+5x2-14x-8 > 0

i hope u can solve this now. :)

62
Lokesh Verma ·

x=2 is a root by observation...

1
The Race begins... ·

ya. shall i solve it too.!!? or let her try this !?

well the final answer is (-4,-1/2) u (2,∞)

correct me if i am wrong !

1
Surbhi Agrawal ·

ohk.. i will try after dis!!![1]

1
Surbhi Agrawal ·

is dis condition sufficient??
i think we need to impose two more conditions!
1. log3 log2 (2x3 + 5x2 - 14x) >0
2. log2 (2x3 + 5x2 - 14x) > 0

106
Asish Mahapatra ·

@surbhi in the steps of solution:
log3log2(2x3+5x2-14x) > 1 so obviously it is >0
and log2(2x3+5x2-14x) > 3 so obviously it is > 0 as well

1
Surbhi Agrawal ·

oh.k...[4]

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