The electric field of an electromagnetic wave in free space is \(\vec{\mathrm{E}}=57\cos \left[7.5\times {10}^{6}\mathrm…

\(\vec{\mathrm{B}}=-\frac{57}{3\times {10}^{8}}\cos \left[7.5\times {10}^{6}\mathrm{t}-5\times {10}^{-3}(3x+4y)\right](\overset{^}{k})\)

\(\vec{\mathrm{B}}=\frac{57}{3\times {10}^{8}}\cos \left[7.5\times {10}^{6}\mathrm{t}-5\times {10}^{-3}(3x+4y)\right](5\overset{^}{k})\)

\(\vec{\mathrm{B}}=-\frac{57}{3\times {10}^{8}}\cos \left[7.5\times {10}^{6}\mathrm{t}-5\times {10}^{-3}(3x+4y)\right](5k)\\\)

\(\vec{\mathrm{B}}=\frac{57}{3\times {10}^{8}}\cos \left[7.5\times {10}^{6}\mathrm{t}-5\times {10}^{-3}(3x+4y)\right](\overset{^}{k})\)