Question 150558
I'll do the first two to get you going in the right direction.


# 1


Good so far until you reach the second to last step


{{{20 = 10x}}}



{{{20/10 = cross(10/10)x}}} Divide both sides by 10.



{{{2 =x}}} Divide 10 into 20 to get 2


So the answer is {{{x=2}}}



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# 2


You're off to a good start, I'll start where you left off.


{{{4 = 5x^2 – x }}} Start with the given equation.



{{{0 = 5x^2 – x -4}}} Subtract 4 from both sides.



Let's use the quadratic formula to solve for x



{{{x = (-b +- sqrt( b^2-4ac ))/(2a)}}} Start with the quadratic formula



{{{x = (-(-1) +- sqrt( (-1)^2-4(5)(-4) ))/(2(5))}}} Plug in  {{{a=5}}}, {{{b=-1}}}, and {{{c=-4}}}



{{{x = (1 +- sqrt( (-1)^2-4(5)(-4) ))/(2(5))}}} Negate {{{-1}}} to get {{{1}}}. 



{{{x = (1 +- sqrt( 1-4(5)(-4) ))/(2(5))}}} Square {{{-1}}} to get {{{1}}}. 



{{{x = (1 +- sqrt( 1--80 ))/(2(5))}}} Multiply {{{4(5)(-4)}}} to get {{{-80}}}



{{{x = (1 +- sqrt( 1+80 ))/(2(5))}}} Rewrite {{{sqrt(1--80)}}} as {{{sqrt(1+80)}}}



{{{x = (1 +- sqrt( 81 ))/(2(5))}}} Add {{{1}}} to {{{80}}} to get {{{81}}}



{{{x = (1 +- sqrt( 81 ))/(10)}}} Multiply {{{2}}} and {{{5}}} to get {{{10}}}. 



{{{x = (1 +- 9)/(10)}}} Take the square root of {{{81}}} to get {{{9}}}. 



{{{x = (1 + 9)/(10)}}} or {{{x = (1 - 9)/(10)}}} Break up the expression. 



{{{x = (10)/(10)}}} or {{{x =  (-8)/(10)}}} Combine like terms. 



{{{x = 1}}} or {{{x = -4/5}}} Simplify. 



So the solutions are {{{x = 1}}} or {{{x = -4/5}}}