Question 40557
{{{R(1) + R(2) = 40}}}
{{{1/R(1) + 1/R(2) = 1/8.4}}}
{{{R^2 -40R + 336 = 0}}}
{{{R = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
{{{R = (40 +- sqrt( (-40)^2-4*1*336 ))/(2*1) }}}
{{{R = (40 +- sqrt( 1600 - 1344 ))/ 2 }}}
{{{R = (40 +- sqrt( 256 ))/ 2 }}}
{{{R = 20 + 8}}}
{{{R = 20 - 8}}}
R = 28,12
check these values
{{{R(1) + R(2) = 40}}}
{{{1/R(1) + 1/R(2) = 1/8.4}}}
{{{28 + 12 = 40}}}
OK
{{{1/28 + 1/12 = 1/8.4}}}
multiply both sides by 4
{{{1/7 + 1/3 = 1/2.1}}}
multiply both sides by 21
{{{3 + 7 = 10}}}
OK