Originally Posted by

**Sally_Math** integrate:-

1. $\displaystyle integral (4x-x^2) ^ (1/2)$ from 0 to 4

i know that I should use completing the square

so i ended up with $\displaystyle (-4-(x-2)^2)^(1/2)$

however, it doesn't look right to me, May I get a helpful solution?

This makes no sense to me, sorry.

Originally Posted by

**Sally_Math** 2.

A certain radioactive isotope is observed to decay to 98% of its initial amount over a

period of one year.

a) Assume that the sample has an initial mass of 100g. Find a function that represents

the mass of a sample as a function of time (in years).

b) What is the half-life of the isotope?

c) How long will it take the sample with initial mass of 100g to decay to a mass of 8g? Try $\displaystyle M = 100\times 0.98^t$ where $\displaystyle t$ is years and $\displaystyle M$ is mass.

For half life sub $\displaystyle M=50$