Find the value of n if `1/8+1/(9 xx 8!)=x/(10 xx 9 xx8!)`

Find the value of n if 1/|_9+1/|_10=n/|_11 .

Find the value of. (3^@ + 4 ^-1) xx 2^2

Find the value of n if ""^nP_6=30 xx ""^nP_4 .

Find the value of. (2^-1 xx 4^-1) div 2^2

Find the value of cos^(-1)("cos"(9pi)/(8)) .

Find the value of x for which the following expressions aquire greatest value ? Also determine their greatest values. 24x-8-9x^2 .