Write the value of 
.
Let 
Expanding along R1,
we get ∆= sin20°cos70°-(-cos20°)sin70°
= sin20°cos70°+cos20°sin70°
Since sin(A+B)= sinAcosB+cosAsinB
Hence, sin20°cos70°+cos20°sin70°=sin(20°+70°)
=sin(90°)
=1
Hence, ∆=1
1
Write the value of .
Let
Expanding along R1,
we get ∆= sin20°cos70°-(-cos20°)sin70°
= sin20°cos70°+cos20°sin70°
Since sin(A+B)= sinAcosB+cosAsinB
Hence, sin20°cos70°+cos20°sin70°=sin(20°+70°)
=sin(90°)
=1
Hence, ∆=1