How do I find Sec(2) with minimal calculator use?

SOLVE STEP BY STEP IN DIGITAL FORMAT The SOLFIES company is dedicated to welding any type of metal, but especially aluminum parts. If the aluminum pieces that are welded come out at 1200°C and to speed up the cooling they are immersed in a tank full of water with a temperature of 0°C. In this case, the heat is transferred from the welded part to the water, causing the temperature to begin to decrease. Taking into account the temperature data of both the piece and the water, in addition to the value of the constant K= 0.02, it is necessary to know how long it takes for the piece to reach a temperature of 20°C in order to handle it and deliver it to the customer. MATH MODEL T'+KT=Tm SOLVED BY THE LAPLACE TRANSFORM METHOD

find the equation of the red line in the picture attached

solve 4cos^2(x)-13cos(x)-12=0 for all solutions 0<=x<2pie