If \(\lim _{\mathrm{x}\to 0}\frac{\cos (2\mathrm{x})+\mathrm{acos}(4\mathrm{x})-\mathrm{b}}{{\mathrm{x}}^{4}}\) is finit…

If \(\lim _{\mathrm{x}\to 0}\frac{\cos (2\mathrm{x})+\mathrm{acos}(4\mathrm{x})-\mathrm{b}}{{\mathrm{x}}^{4}}\) is finite, then \((\mathrm{a}+\mathrm{b})\) is equal to :

[JEE Main 2025, 2 Apr (Shift 2)]