This is an expression, not an equation, because there’s no equals sign. Also, what is meant by “1/2^l3”? Does l3 mean l³?
If we assume that l is a lowercase L, which can be represented by ℓ, and we assume the expression is equal to zero, then:
-ℓ²+2ℓ-½^(ℓ³)=0.
This has the approximate solution, ℓ=0.61453.
If the third term should have been 1/2l^3 then the problem simplifies:
-ℓ²+2ℓ-½ℓ³=0, ℓ² -2ℓ+½ℓ³=0, ℓ³+2ℓ²-4ℓ=ℓ(ℓ²+2ℓ-4)=0, so ℓ=0, -1+√5, -1-√5.