Can someone please help me with this math problem

In the surface area formula for cylinders which expressionrepresents the lateral area

What number should be added to both sides of the equation to complete this square? x^2-10x=7

Si la base de un triángulo isósceles mide 70 m y el ángulo opuesto a ésta mide 58°; entonces ¿cuánto mide la altura de dicho triángulo? a) 21.87 m. b) 40.01 m. c) 43.74 m. d) 63.14 m.