kelman90
Member

Given x^2+bx+2c=0
What value in terms of c must b have to make this expression a perfect square?

Yeah
Member

polonium210 is a radioactive element with a halflife of 140 days. This means that half of the polonium decays every 140 days. If 400 mg is the initial sample how much is left after 700 days?

ÜberMathGuru
Member

Yeah,
Sorry for the delayed response!
The basic equation for half life is
AT = A0 2^(T/H)
where A0 is the initial radioisotope’s activity, AT is the decayed activity after time T, and H is the halflife.
These values in your problem would be:
A0=400 mg
H=140 days
T=700 days
and AT is what they are asking for.
AT=400x[2^(700/140)]=400×2^(5)= 400x (1/2^32) = 400/32= 12.5 mg

butler
Member

what are all the variables of a graph

ÜberMathGuru
Member

(x^2y^4)^2=x^4y^8
Always multiply the outer exponent by the exponent of each factor (or by both the exponent of the numerator and the denominator if it is a ratio)!!!!
