Math Is Fun Forum

ok i know how to solve system of equations but with this one i am having problems !

1) a - b = 1
2) b - 2c = 1
3) 3a - 4c = 7

ok i know that
you have to first
1equation subtract 2equation
and then
2equation plus 3equation
i know that
but you see that in each equation one letter is missing
so how can we
subtract a-b=1 from b-2c=1
is we dont have a or c????

and same goes for the second part

help:/

find the inverse function of
y =  2x + 2

original function
y = 2x + 2

rearranged
2x = y - 2

solved for x
x = 1/2y - 1/2

inverse function changed x to y and y to x
y = 1/2x - 1/2

correct
yes no?

use the quadratic formula to find the roots of the equation
3x^3 - 2x + 5 = 0

i did

formula :
       -b +- sqrt (b^2 - 4ac)
x = ----------------------------
               2a

        - (-2) +- sqrt( (-2)^2 - 4(3)(5) )
x = ----------------------------------------
                2(3)

        2 +- sqrt (-4 - 4(15) )
x = ------------------------------
              6

         2 +- sqrt ( -4 - 60)
x = ------------------------------
                6

         2 +- sqrt ( -64 )
x = ---------------------------
               6

now what i do i forgot?