# Simple? Think again.

If 7^x = 16y and 4^x = 49y then find the value of y-x . Note by Gaurav Sharma
5 years, 2 months ago

This discussion board is a place to discuss our Daily Challenges and the math and science related to those challenges. Explanations are more than just a solution — they should explain the steps and thinking strategies that you used to obtain the solution. Comments should further the discussion of math and science.

When posting on Brilliant:

• Use the emojis to react to an explanation, whether you're congratulating a job well done , or just really confused .
• Ask specific questions about the challenge or the steps in somebody's explanation. Well-posed questions can add a lot to the discussion, but posting "I don't understand!" doesn't help anyone.
• Try to contribute something new to the discussion, whether it is an extension, generalization or other idea related to the challenge.

MarkdownAppears as
*italics* or _italics_ italics
**bold** or __bold__ bold
- bulleted- list
• bulleted
• list
1. numbered2. list
1. numbered
2. list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1paragraph 2

paragraph 1

paragraph 2

[example link](https://brilliant.org)example link
> This is a quote
This is a quote
    # I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
# I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
MathAppears as
Remember to wrap math in $$ ... $$ or $ ... $ to ensure proper formatting.
2 \times 3 $2 \times 3$
2^{34} $2^{34}$
a_{i-1} $a_{i-1}$
\frac{2}{3} $\frac{2}{3}$
\sqrt{2} $\sqrt{2}$
\sum_{i=1}^3 $\sum_{i=1}^3$
\sin \theta $\sin \theta$
\boxed{123} $\boxed{123}$

Sort by:

2.001

- 5 years, 2 months ago

7^x=16y...(1) 4^x=49y....(2) 4rm equation (2)....y=4^x/49 substitutin y=4^x/49 in equation(1) 7^x=164^x/49 7^x49=164^x 7^x7^2=16*4^x 7^(x 2)=2^(2x 4)...(4rm law of indicies) take log of both sides (x 2)log7=(2x 4)log2 (x 2)0.845=(2x 4)0.3010 0.845x 1.69=0.602x 1.204 0.845x-0.602x=1.204-1.69 0.243x=-0.486 x=-0.486/0.243 x=-2 usin equation(2) 4^x=49y y=4^x/49 substitutin x=-2 y=4^-2/49 y=1/16/49 y=0.00138 since x=-2 and y=0.00138 y-x=0.00138-(-2) y-x=0.00138 2 y-x=2.00138

- 5 years, 2 months ago

Awesome ! But try solving it by logic ( it's much easier )

- 5 years, 2 months ago

@sharma.......logic? hmm....that good

- 5 years, 2 months ago

Yea..because you can't find the exact ( perfect ..and not approximate )value of y by log ..but you can find it in one step by logic

- 5 years, 2 months ago

- 5 years, 2 months ago

Nope..studious guys in India prefer to be away from such vices

- 5 years, 2 months ago

@sharma....(lafin) that good.....do u knw any other educative wapsite or website other than brilliant?

- 5 years, 2 months ago

I don't know ..

- 5 years, 2 months ago

@sharma...ok..no prob

- 5 years, 2 months ago

@ayanlaja..you are in which grade / standard presently ?

- 5 years, 2 months ago