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substr(): Passing null to parameter #1 ($string) of type string is deprecated /home/refseek1/public_html/search2/include/func-common.php:23

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substr(): Passing null to parameter #1 ($string) of type string is deprecated /home/refseek1/public_html/search2/searchdoc.php:24

site:www.shsu.edu/kws006/Precalculus/4.8_Trig_Identities_ - RefSeek