Knowing the Pythagorean triplets comes in handy: 5,12,13 (when we know the difference between two sides is 1 cm).
You can also find it using the Pythagorean theorem:
AB2+BC2=AC2
Let's say AB=x, then AC=x+1 (since AC−AB=1)
Using Pythagorean theorem:
x2+25=(x+1)2
x2+25=x2+2x+1
25=2x+1
24=2x
x=12
Therefore:
AB=12 cm
AC=13 cm
BC=5 cm
Find sin(C) and cos(C):
sin(C)=ACAB=1312
cos(C)=ACBC=135
Substituting into the expression:
1+cos(C)1+sin(C)=1+1351+1312=13+513+12=1825