Ok

arsinh4 = ln(4+ 17^1/2 )

cosh (arsinh4)

cosh (ln (4 + 17^1/2 ) = 1/2(e^ln(4 + 17^1/2 ) + e^-ln(4 + 17^1/2 ))

cosh (ln (4 + 17^1/2 ) = 1/2( 4+17^1/2 - 1/(4 + 17^1/2 )

cosh (ln (4 + 17^1/2 ) = 1/2 ( ((4+17^1/2)^(2) -1))/(4 + 17^1/2)

= ( 16 + 8(17)^1/2 + 17 -1 )/(4 + 17^1/2 )

= ( 32 + 8(17)^1/2 )/(4+17^1/2)

multiply with (-4+17^1/2)/(-4+17^1/2)

= ( 32(17)^1/2 + 8(17) - 4(32) - 4*8(17)^1/2 )/(17 - 16 )

= (136 - 128 )/1 =

you continue