Show that every map of $S^{k + l} \rightarrow S^k \times S^l$ induces the given trivial homomorphism.

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Here is the question:

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Could anyone give me a hint on how to do so please?

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Hint: first use the cup product structure to determine that $f^*$ is trivial. Then use naturality of the short exact sequence $$0\to \operatorname{Ext}(H_{k+\ell-1}(X),\Bbb Z)\to H^{k+\ell}(X)\to \operatorname{Hom}(H_{k+\ell}(X),\Bbb Z)\to 0$$ to get the result.

As to the second part, there must be a typo because there are no such maps $S^2\to S^1\times S^1$ (since $\pi_2(S^1\times S^1)=0$).