SU(3)E-invariant form factor for pseudoscalar mesons

The use of a form factor which is invariant with respect to the spectrum-generating SU(3) leads to a definition for the strangeness-changing suppression factor for $K_{l_3}$ decay which is numerically equal to the strangeness-changing suppression factor for $K_{l_2}$ decay and close to $\frac{m_{\pi }}{m_K}$. It also predicts the electromagnetic radius of the pseudoscalar mesons in terms of ${\lambda }_{+}$.